Automatic switch



Nov. 22, 1938. R. TAYLOR ET AL 4 2,137,423 I AUTOMATIC SWITCH Filed (Wt. 51, 1935 2 Sheds-Sheet 1 JM/EA QRS- flaw/1w 72mm? 650/? 7/70/1445 BAKER.

Nov. 22, 1938. i

R. TAYLOR ET AL 2,137,423

AUTOMATIC SWITCH Filed Oct. 31, 1935 I IEEIIHIHI+ 2 Sheets-Sheet 2 mum? Res/Mew Z nioR GEORGE 7/'/oM4s BAKER Patented Nov. 22, .1938

UNITED STATES PATENT OFFICE AUTOMATIC SWITCH Application October 31, 1935, Serial No. 47,538

In Great Britain November 23, 1934 8 Claims.

The present invention relates to automatic switches for use in telephone or like systems and is more particularly concerned with switches of the two-directional type arranged to be set as regards the first movement in response to impulses and thereafter to hunt for an idle line in the group selected. The invention moreover contemplates the use of switches of the so-called large capacity type in which hunting takes place simultaneously over a plurality of sets of wipers and it is desirable to ensure that if a plurality of wipers engage idle lines simultaneously there shall be a definite order of priority in which they are taken into use.

According to one feature of the invention in an automatic switch arranged to hunt for an idle line, a relay controlling the drive circuit for the magnet eifecting the hunting operation is energized during the said operation and by its deenergization opens the magnet circuit and applies guarding potential to the selected line.

According to another feature of the invention in an automatic switch arranged to test simultaneously over a plurality of test wipers for an idle line, the test relays associated respectively with the various test wipers are arranged to be all energized during the hunting operation while when any test wiper encounters an idle line its test relay is de-energized and the drive circuit for the operating magnet broken thereby.

A further feature of the invention is that in an automatic switch provided with two sets of wipers and arranged to perform a hunting operation during which testing for an idle line takes place over both sets of wipers simultaneously, during the hunting operation both the test relays associated with the respective test wipers are energized each relay being arrangedto release when its associated wiper encounters an idle line, while if both relays release due to two idle lines being encountered simultaneously a circuit is subsequently completed for one particular relay only so that one set of wipers is always given definite preference. I

Another feature of the invention is that in an automatic switch arranged to be set by impulses to select a particular group of lines and thereafter to hunt automatically for an idle line in the selected group, a relay energized when the switch is taken into use serves to operate the test relay as soon as the switch moves off-normal and is de-energized at the end of the group selecting movement to initiate the hunting movement, the test relay being de-energized when an idle line is found and again completing a circuit for the first relay which thereupon again energizes the test relay and switches the wipers through.

According to a further feature of the invention in an automatic switch arranged to perform a hunting operation the relay which by its deenergization initiates the hunting movement is arranged to be re-operated on the termination of the hunting and when subsequently released initiates the restoration of the switch to normal and guards it against seizure until normal posi tion is reached.

Still another feature of the invention is that in an automatic switch arranged to hunt for an idle line when an idle line is found a relay deenergizes due to the absence of busy potential on the test contact and on releasing applies busy potential to the contact to prevent seizure of the line by a similar hunting switch having access thereto.

If the switch is arranged for the known systern in which earth is employed to indicate the engaged condition and the absence of earth indicates that a line is free, the invention offers the additional advantage that if a test contact should have booster battery connected to it owing to a metering operation taking place at that instant, this will have the same effect as the normal busy earth and there is no danger of the switch seizing the line or operating improperly. Furthermore a high resistance earth which might not permit the operation of a relay is sufficient to maintain it operated so that the switch will not seize a line thus marked.

The invention will be better understood from the following description of one method of carrying it into effect which shouldbe taken in conjunction with the accompanying drawings, Figs. 1 and 2. These are diagrammatic circuit drawings and show the invention applied to a vertical and rotary switch of the mechanical construction disclosed in Patent No. 2,028,689, granted Jan. 21, 1936, which switch is arranged to have two sets of wipers each having access to 100 outlets. The operation of the switch is that in response to the controlling train of impulses the wipers are stepped vertically and then perform a rotary hunting movement. Release is effected by reenergizing the rotary magnet whereupon the switch advances to the end of the bank, drops clear and then rotates back to normal under spring tension.

Referring now to the drawings, when the switch is taken into use a loop is placed across the negative and positive conductors, which operates relay A and in turn relay B. If the switch is functioning as a first selector, the earth to the lower winding of relay A may be supplied by way of a dial tone transformer, in order that the calling subscriber may be informed when the circuit is in readiness to respond to the dialled impulses. Relay B upon operating, at armature bl connects earth to the release trunk conductor P to guard the switch and at armature b2 operates relay C over its lower winding which is of high resistance.

Relays B and C together prepare a number of circuits the effect of which will be appreciated subsequently, but no further change takes place due to the seizure of the switch.

Upon the reception of the setting impulses, relay A responds and repeats them by way of armature al to the vertical magnet VM in series with the upper low resistance winding of relay C and accordingly the wipers are raised to the desired level. As soon as the wipers leave the normal position, the oil-normal springs are mechanically operated, thereby at springs N2 extending earth from rel-ease trunk conductor P to operate relays HA and HB over their righthand windings. These relays at armatures ha l and M24 short-circuit the lower winding of relay C but it will be understood that this relay remains operated during impulsing owing to the intermittent energization of its upper winding in circuit with the vertical magnet and the slugging effect of its short-circuited winding. Relay B similarly remains operated by reason of the copper slug surrounding its core.

At the end of the train of impulses relay A remains operated and after a short period relay C releases and at armature 03 connects the righthand winding of relay HB to the test Wiper PI. The righthand winding of relay HA is already connected to the test wiper P2 over its own armature M13 and the armature hb3. Moreover, at armature 04 a circuit is completed for the rotary magnet RM in series with its interrupter contacts rm to earth on the release trunk conductor P, so that the wipers are advanced into engagement with the first set of contacts in the level selected. Rotary off-normal springs NRI to NBA are mechanically operated as soon as the wipers commence to rotate and disconnect various circuits which are no longer required after the commencement of the rotary movement.

If both outlets now engaged are busy, relays HA and HB will be maintained by earth picked up by the test wipers after the circuit to their lefthand windings is disconnected by the opening of the interrupter contacts rm. Accordingly after the rotary magnet releases due to the opening of the interrupter contacts and these contacts therefore close, the magnet is again energized to advance the wipers on to the second set of contacts. It will be noticed that while the wipers are moving from contact to contact relays HA and HB are held over their lefthand windings in parallel with the rotary magnet. This stepping operation continues automatically until an idle line is found, or alternatively the. wipers are advanced to thellth position.

If wiper P2 is the first to encounter a free outlet, relay HA will restore when the interrupter contacts open, and at armature hat cuts the drive circuit to the rotary'magnet to prevent further movement of the wipers, and at armature hafi extends earth to wiper P2 and the test provided to the centre winding of relay HB to maintain it operated.

It will be remembered that while relays HA and HB were both operated, the lower winding of relay C was short-circuited, but when relay HA de-energizes the short-circuit is removed and relay C re-operates, thereupon switching the speaking leads through to the lower set of wipers. Relay A is now disconnected since the rotary off normal contacts NR3 and NR4 have opened and on releasing it opens the circuit of relay B. Shortly afterwards therefore, relay B releases but relay HIB remains operated by earth on the release trunk conductor which has been extended back from the succeeding switch over the P2 wiper. Relay C also remains operated after the release of relay B by the energization of its lower winding over the operated armature hbd and the resting armature ha l.

If however, the Pl wiper is the first to encounter a free outlet, relay HB immediately releases to guard the outlet selected, and disconmeets the driving circuit for the rotary magnet. Relay HB also releases relay HA but upon the operation of relay C as described above relay HA is re-operated over its middle winding and accordingly switches the connection through to the upper set of wipers.

In case both test wipers encounter free outlets simultaneously, both testing relays HA and HB restore, whereupon relay C energizes and reoperates relay HA to switch the connection through over the upper set of wipers. In these circumstances, therefore, it is clear that priority will always be given to the upper set of wipers.

If all outlets in the level selected prove busy, the wipers are rotated to the 11th position where cam springs SI to S3 are mechanically operated, thereby at springs SI releasing relay HB and connecting earth to the test wiper PI to operate the overflow meter not shown, but assumed to be connected to conductor l0. Relay HB on releasing brings down relay HA but when relay C operates it re-operates relay HA to switch the upper set of wipers through to the 11th step contacts which are multipled together and connect with the windings of relay A. Furthermore, at cam springs S2 busy flash and tone from the cam assembly ET is extended through the lower winding to relay A and the 11th contact, wiper I to the positive line to inform the calling subscriber that the connection is unavailable. During the flash period relay A is released, but owing to the closure of cam springs S3 relay B is held over its lefthand winding by battery supplied from the cam assembly BH.

Upon the release of the connection at the end of the conversation, earth is removed from the release trunk conductor P and relay HA or relay HB, as the case may be releases. This opens the circuit for relay C which de-energizes in its turn, and at armature c4 completes a self-interrupted driving circuit for the rotary magnet RM to the common conductor H extending to release alarm equipment. Accordingly the wipers are rotated clear of the banks, after which they fall and then rotate below the banks under spring tension back to their normal position, where the off normal springs NI open the homing circuit. Preferably during the vertical release movement of the wipers, the rotary magnet is mechanically prevented from opening its interrupter contacts, so that there is no tendency for it to chatter. The armature b6 provided in the circuit of relay A ensures non-interference with the selector during release.

During the release period the switch is guarded by the application of earth to the release trunk conductor P over armature cl and off normal springs N2, but it will be noted that at the commencement of release an initial unguard is provided to enable preceding switches to restore,

this period being represented by the sum of the release time of relay BA or relay HB and that of relay C. Itis found that this time may be adjusted with some degree of accuracy and therefore the unguard during release may be regarded as substantially constant and is conveniently ,of the order of 25 milliseconds.

In case for any reason the switch fails to restore, the off normal springs NI remain closed, and as a result of the prolonged connection of battery to conductor 1 I, the release alarm equipment functions after a delay period and provides an indication of the faulty condition.

It should be mentioned that at armature hb5 a circuit is prepared to the common conductor l2 extending to a test buzzer, which may be operated by short circuiting the test jack springs T2. This enables the set of wipers in use to be determined without the need for removing the dust cover from the switchand examining the actual re-' lays. lamp LP which is lighted in circuit with a common conductor I3 extending to exchange alarm equipment, which provides a signal in case the switch is seized but not operated within a predetermined time.

The terminals marked TI to T8 in the drawings are assembled in the form of a test jack located at the front of the switch to facilitate testing. The condenser QA and the associated resistance are provided as usual in the magnet circuits for spark quenching purposes.

According to the invention therefore, an improved group selector switch has been designed in which by arranging for the test relays to deenergize when an idle line is encountered, the unguarded interval has been almost completely eliminated and moreover the switch operates satisfactorily if it encounters a high resistance earth or booster battery which serves as a definite busy indication. A further advantage is that there is definite priority of switching without any complicated sets of contacts which require very careful adjustment.

We claim:

1. In a selector switch, a driving magnet, a

ing it to stop the switch when the relay deenergizes, and contacts on said relay closed by the deenergization thereof for placing a busy potential on the test contact of the selected trunk.

2. In a selector switch having two sets of wip- The switch as shown is provided with a ers, each set including a test wiper, means for operating said switch to search for an idle trunk with both sets of wipers, two test relays held energized over the two test wipers, respectively, only so long as busy trunks are encountered, and contacts on each test relay for stopping the switch and for placing a busy potential on its associated test wiper when such wiperfinds an idle trunk.

3. In a selector switch having two sets of wipers, each set including two talking circuit wipers and a test wiper, means for operating the switch to search for an idle trunk with both sets of wipers, two test relays held energized over the two test wipers, respectively, so long as said wipers encounter busy trunks, contacts on each test relay for stoppingthe switch when the relay deenergizes responsive to its associated test wiper finding an idle trunk, and means efiective when any test wiper finds an idle trunk for completing talking circuit connections to the associated talking circuit wipers, said connections including contacts of the deenergized test relay and also contacts of the other test relay in energized condition.

4. In a selector switch, means for operating said switch to search for an idle trunk, a test relay deenergized to stop the switch when an idle trunk is found, means for reoperating said relay to connect up the talking circuit wipers of the switch, and means for preventing the reoperation of said relay from restarting the switch.

5. In a selector switch, two sets of wipers, each set including talking circuit wipers and a test wiper, 'two test relays controlled over the two test wipers, respectively, and contacts on each test relay effective when the relay is energized to connect up the talking circuit wipers of the set whose test wiper is associated with the other test relay.

6. In a selector switch having primary and secondary movements, a combined changeover and switching relay, means for energizing said relay during the primary movement and for deener-- gizing it at the end of the primary movement to start the secondary movement, and means for energizing said relay at the end of the secondary movement to close the talking circuit through to the wipers of the switch.

'7. In. a twomotion selector switch, a line relay, a switching relay for disconnecting the incoming line from said line relay and for extending the line through to the switch wipers upon the completion of the operation of the switch, means for utilizing said switching relay as, a changeover relay, and secondary off-normal contacts for preventing the energization of said switching relay when used as a changeover relay from disconnecting said line relay.

8. In a selector switch of the searching type, two sets of wipers, a switching relay common to both wiper sets, two test relays, a circuit for said switching relay, and contacts on said test relays for maintaining said switching relay short circuited to prevent its energization while the selector is searching for an idle trunk.

REGINALD TAYLOR.

GEORGE THOMAS BAKER. 

